Restricting excess bandwidth use by including a passive RC filter before the ADC results in better SNR and THD. However, restricting the bandwidth too much results in a excessive operational amplifier settling time. If the amplifier output does not settle quick enough, some residual charges from the previous channel remain in the next sampling interval and appear as crosstalk. One approach to solve this settling issue is to reduce the throughput of the ADC. However, the high sample rate ADC is often selected to meet the need to acquire higher frequency signals, limiting the freedom to reduce the ADC throughput. Due to these tradeoffs, the choice of the filter capacitor becomes critical. Figure 7-6 and Figure 7-7 show SNR and crosstalk as a function of the filter capacitor.

Figure 7-8 shows input settling behavior with three different filter capacitor values. The value of the capacitor changes to filter bandwidth. As the filter bandwidth increases, the settling time improves as shown in Equation 4.